Shares of Laboratory Corporation of America Holdings dropped more than 5 percent Monday after a report said the medical lab operator is in talks to acquire privately held contract researcher Pharmaceutical Product Development for more than $8 billion, including debt.

The North Carolina-based company's deal would be its largest acquisition ever and would help its strategy of combining testing services under one roof, according to Reuters, citing people familiar with the matter.

A spokesperson for Laboratory Corp told CNBC the company "does not comment on market rumors."

In 2015, Laboratory Corp acquired research organization Covance for about $5.7 billion. PPD was taken private in 2011 for $3.9 billion.